Field of the Invention
The present disclosure relates to a flexible organic light emitting display device, and more particularly, to a flexible organic light emitting display device having a flexible encapsulation unit with improved flexibility.
Discussion of the Related Art
Display devices capable of displaying information have been rapidly developed. Research for improving performance, minimizing thickness, reducing weight, and lowering power consumption has been continued. As representative examples of the display devices, a liquid crystal display device (LCD), a plasma display panel device (PDP), a field emission display device (FED), an electro-wetting display device (EWD), an organic light emitting display device (OLED), and the like may be included.
In particular, unlike a liquid crystal display device, since an organic light emitting display device is a self-emission type of display, it does not require a separate light source. Thus, the organic light emitting display device can be manufactured in lightweight and thin form factors. Further, the organic light emitting display device is advantageous in terms of power consumption and is excellent in response speed, viewing angle, and contrast ratio. Therefore, the organic light emitting display device is considered as a next-generation display. However, in spite of these advantages, since the organic light emitting display device is particularly vulnerable to moisture and oxygen, the organic light emitting display device may have a problem in that it is difficult to secure manufacturing reliability than other display devices.
The organic light emitting display device typically includes an organic light emitting element constituted by an anode, an organic light emission layer, and a cathode. In the case of a top-emission type organic light emitting display device, the cathode has a transparent or translucent characteristic and the anode has a reflective characteristic in order to provide the light emitted from the organic light emission layer in an upward direction. Herein, holes provided in the anode and electrons provided in the cathode are coupled to emit light, and as a result, the organic light emission layer is vulnerable to moisture or oxygen. In detail, when moisture or oxygen permeates from the outside of the organic light emitting display device, the organic light emission layer is transmuted, and as a result, various failures including dark spot formation, pixel shrinkage, and the like can occur. Therefore, in order to secure the reliability of the organic light emitting display device, a transparent encapsulation unit for protecting the organic light emitting element from oxygen and moisture is used on the organic light emitting element.
In particular, since the organic light emitting display device is vulnerable to oxygen and moisture, the encapsulation unit of the organic light emitting display device is desired to have a higher performance level with respect to delaying or minimizing oxygen and/or moisture permeation than other types of electronic devices, such as liquid crystal display devices, plasma display panel devices, field emission display devices, electro-wetting display devices, solar cells, lithium ion batteries, sensors, and memory semiconductors.
In particular, it is difficult to develop an encapsulation unit of an organic light emitting display device which can be mass-produced while solving the aforementioned problems under a situation in which reliability, yield, process time, process difficulty, cost, and the like are related with each other in a trade-off relationship.
In recent years, a flexible organic light emitting display device has attracted attention as a next-generation display device. Flexible OLEDs allow for images to be properly displayed even if the substrate is curved, bent, folded, flexed, rolled, or otherwise manipulated in some non-planar forms.
Flexible organic light emitting displays have diverse applications, from personal portable devices to computers monitors and large screen TVs. Much research with respect to flexible OLEDs having reduced size (thickness) and weight in addition to a large display area has been in progress.
However, in the aforementioned general encapsulation unit configuration, since the thickness of the encapsulation unit is relatively large, an inorganic encapsulation layer of the encapsulation unit can be easily cracked or damaged by a stress generated by bending or folding a flexible organic light emitting display device.
Further, foreign matters, debris, undesired particles, etc. may be undesirably introduced onto the inorganic encapsulation layer during the manufacturing process. For example, if a bonding process is performed by using an adhesive layer attached to the inorganic encapsulation layer, a portion of the inorganic encapsulation layer may be pierced by a foreign matter. As a result, moisture and/or oxygen permeates into the organic light emission layer where piercing, imprinting, or punching phenomenon occurs, and as a result, dark spots or other detrimental effects may occur.
Meanwhile, since the encapsulation unit of the organic light emitting display device is formed after the organic light emission layer is formed, there may be limitations in the manufacturing process. For example, since the organic light emission layer is vulnerable to heat, the encapsulation unit is desired not to be formed by any process requiring a temperature above a certain level.